Traditional field effect transistors (FET's) are familiar conventional devices commonly incorporated as a fundamental building block into the intricate circuitry of integrated circuit (IC) chips. Downward scaling of FET dimensions has improved circuit performance and increased the functional capability of FET's packed on an IC chip. However, continued reductions in device dimensions may be hampered by the size limitations imposed by traditional materials and the costs associated with lithographic patterning to define device features.
Carbon nanotubes are nanoscale high-aspect-ratio cylinders consisting of hexagonal rings of carbon atoms that may assume either a semiconducting electronic state or a conducting electronic state. Semiconducting carbon nanotubes have been used to form hybrid devices, such as hybrid FET's. In particular, FET's have been fabricated using a single semiconducting carbon nanotube as a channel region and forming ohmic contacts at opposite ends of the semiconducting carbon nanotube extending between a gold source electrode and a gold drain electrode situated on the surface of a substrate. A gate electrode is defined in the substrate underlying the carbon nanotube and generally between the source and drain electrodes. An oxidized surface of the substrate defines a gate dielectric situated between the buried gate electrode and the carbon nanotube. Such FET's should switch reliably while consuming significantly less power than a comparable silicon-based device structure due to the small dimensions of the carbon nanotube.
Synthesized carbon nanotubes randomly form in a mixture or collection of conducting and semiconducting electronic states when grown by conventional synthesis processes. Unfortunately, no conventional synthesis process is capable of exclusively growing semiconducting carbon nanotubes or, for that matter, growing only conducting carbon nanotubes. Therefore, semiconducting carbon nanotubes and/or conducting carbon nanotubes must be individually sorted by a painstaking post-synthesis operation from commingled mixtures of conducting and semiconducting carbon nanotubes. The inability to effectively separate nanotubes of different electronic states has hindered the maturation of carbon nanotube hybrid device structures.
What is needed, therefore, is a method of effectively removing conducting carbon nanotubes from a random collection of conducting and semiconducting carbon nanotubes.